Wireless communication systems following Universal Mobile Telecommunications Systems (UMTS) technology, were developed as part of Third Generation (3G) Radio Systems, and is maintained by the Third Generation Partnership Project (3GPP). A typical UMTS system architecture in accordance with current 3GPP specifications is depicted in FIG. 1. The UMTS network architecture includes a Core Network (CN) interconnected with a UMTS Terrestrial Radio Access Network (UTRAN) via an Iu interface. The UTRAN is configured to provide wireless telecommunication services to users through wireless transmit/receive units (WTRUs), referred to as user equipments (UEs) in the 3GPP standard, via a Uu radio interface. A commonly employed air interface defined in the UMTS standard is wideband code division multiple access (W-CDMA). The UTRAN has one or more radio network controllers (RNCs) and base stations, referred to as Node Bs by 3GPP, which collectively provide for the geographic coverage for wireless communications with UEs. Uplink (UL) communications refer to transmissions from UE to Node B, and downlink (DL) communications refer to transmissions from Node B to UE. One or more Node Bs are connected to each RNC via an Iub interface; RNCs within a UTRAN communicate via an Iur interface.
According to 3GPP standard Release 6 for high speed uplink packet access (HSUPA), the MAC layer multiplexes higher layer data into MAC-e PDUs. In a transmission time interval (TTI), the MAC layer sends one MAC-e PDU to the PHY layer to be transmitted over the enhanced dedicated channel (E-DCH) dedicated physical data control channel (E DPDCH). As part of link adaptation, the MAC layer performs enhanced transport format combination (E-TFC) selection based on radio link control (RLC) logical channel priority, RLC buffer occupancy, physical channel conditions, serving grants, non-serving grants, power limitations, hybrid automatic repeat request (HARQ) profile and logical channel multiplexing.
As part of the E-TFC selection function, the UE initially identifies the highest priority higher layer MAC-d flow that has data to be transmitted. The UE then identifies the MAC-d flow(s) which are allowed to be multiplexed with this MAC-d flow and whose grants allow them to transmit in the current TTI. Based on the HARQ profile of the selected MAC-d flow, the UE identifies the power offset to use for transmission. Based on this power offset and the E-TFC restriction procedure, the MAC determines the maximum supported MAC-e PDU size or E-TFC that can be sent by the UE, called the maximum supported payload, for the upcoming transmission, based only on available power, without taking into account available serving and/or non-serving grants. The E-TFC selection algorithm then determines the largest amount of data, called the scheduled payload, that can be transmitted based on the serving grant and the selected power offset. In the case of non-scheduled flows, the E-TFC selection algorithm takes into account the non-scheduled grant to determine a non scheduled payload. The total granted payload is equivalent to the determined scheduled and non-scheduled payload, and is defined as the amount of data that the UE is allowed to transmit based on serving and non-scheduled grants. However, due to the fact that the UE may have limited power, the available amount of data that the UE can transmit (available payload) is the equivalent of the minimum value between the maximum supported payload and the total granted payload.
Once the available payload is determined, the MAC layer requests data from the logical channels corresponding to the MAC-d flows that are allowed to be multiplexed in the current TTI in order of priority. When all the data to fill a MAC-e PDU according to the available payload is available, or when no more RLC data is available, the MAC-e PDU is sent to the physical layer to be transmitted over the E-DPDCH with the selected beta factor, which is a gain factor.
According to 3GPP standard Release 6, the radio link control (RLC) layer in acknowledged mode (AM) can only operate using fixed RLC protocol data unit (PDU) sizes. In addition, the high-speed medium access control (MAC-hs) entity in the Node B and the medium access control (MAC-e/es) entity in the UE do not support segmentation of the service data units (SDUs) from higher layers. These restrictions may result in performance limitations, especially as high speed packet access (HSPA) evolves towards higher data rates. In order to reach higher data rates and reduce protocol overhead and padding, a number of new features were introduced to the layer 2 (L2) protocol in 3GPP Release 7. In particular, flexible RLC PDU sizes and MAC segmentation in the downlink were introduced. However, corresponding L2 enhancements were not introduced for uplink operation in 3GPP Release 7.
More recently, a new 3GPP work item has been proposed for Improved L2 Uplink to introduce enhancements to L2 operation in the uplink. Some of the objectives of Improved L2 Uplink include: support for flexible RLC PDU sizes; support for MAC segmentation of higher layer PDUs including MAC-d and MAC-c PDUs; smooth transition between old and new protocol formats; and support for seamless state transitions between the CELL_DCH, CELL_FACH, CELL_PCH and URA_PCH states, dependent on potential enhancements to the CELL_FACH uplink transmission.
The current E-TFC selection algorithm is designed for current 3GPP standards releases, including Release 7 or earlier, and the current enhanced dedicated channel (E-DCH) functionalities, which require fixed RLC PDU sizes. It is recognized that current E-TFC selection algorithm for Release 7 or earlier will result in inefficient creation of MAC-e/es PDUs under the proposed Improved Layer 2 Uplink because the current E-TFC selection algorithm is not designed to take into account flexible RLC PDU sizes for every logical channel, segmentation of RLC PDUs, and flexible header format size based on the amount of RLC PDUs in a enhanced MAC-es PDU.
Therefore, a new E-TFC selection function that takes into consideration the additional functionalities including flexible RLC PDU size, segmentation of RLC PDUs and flexible header format size when creating a MAC-e PDU with optimal RLC PDU sizes is desired.